1. Field of the Invention
The present invention relates to a display device having a capacitance-type touch panel, and particularly to a technique that is effective in preventing false operations at peripheral portions of the touch panel.
2. Description of the Related Art
A display device equipped with a device (hereinafter, also referred to as a touch sensor or a touch panel) for inputting information on a display screen with a touch operation (touch and press operation, hereinafter, simply referred to as touch) using a finger of a user or a pen is used in mobile electronic devices such as PDAs and mobile terminals, a wide variety of home electric appliances, automated teller machines, and the like. There have been known a resistive film-type touch panel for detecting changes in resistance values at a touched portion, a capacitance-type touch panel for detecting changes in capacity at a touched portion, and an optical sensor-type touch panel for detecting changes in the amount of light.
For example, Japanese Unexamined Patent Application Publication No. 2003-511799 discloses such a capacitance-type touch panel. In the capacitance-type touch panel disclosed in
Japanese Unexamined Patent Application Publication No. 2003-511799, electrodes (X-electrodes) for detection in the vertical direction and electrodes (Y-electrodes) for detection in the horizontal direction that are arranged in a two-dimensional matrix are provided to detect the capacity of each electrode with an input processor. In the case where a surface of the touch panel is touched with a conductor such as a finger, the capacity of each electrode is increased. Thus, the increase is detected by the input processor and the input coordinates are calculated on the basis of a signal of changes in capacity detected at each electrode.
As a general structure of a conventional capacitance-type touch panel, a front panel is entirely attached to a front surface of the capacitance-type touch panel using adhesives. The front panel is formed on the uppermost layer and is accordingly exposed. Thus, the front panel is scratched or tainted, and needs to be exchanged.
However, when exchanging the front panel, the touch panel also needs to be exchanged in the conventional structure. Thus, there have been requests to exchange only the front panel. In order to respond to the requests, it is only necessary to attach the front panel and the capacitance-type touch panel to each other only at peripheral portions, and thus only the front panel can be easily exchanged with this structure.
However, in the capacitance-type touch panel with the structure in which the front panel and the touch panel are attached to each other only at the peripheral portions, when the front panel is pressed relatively hard, the interval between the front panel and the touch panel becomes narrow or wide because the peripheral portions of the touch panel are fixed to the front panel using the adhesives.
In this case, the capacitance-type touch panel also detects changes in the thickness of an interval layer (a so-called air layer) between the front panel and the touch panel, and thus false reaction possibly occurs at the peripheral portions of the touch panel, leading to false operations.